It is known to use plastic containers in the food preparation and restaurant industry to package prepared foods. The typical food container of the prior art consists of a clear or solid colored base and a clear lid. In order to maintain the quality of food contents and prevent tampering with the contents of a sealed container, it is desirable that the food container, once initially sealed, not be capable of being initially opened without visible indication of the container having been opened. To achieve this feature, container manufacturers have designed containers having integral tamper evident features. Typically, these containers consist of a lid that is hingedly attached to a base. The lid seals to the base by superposing the rim of the lid upon the rim of the base. These types of plastic containers are sold as one-piece containers and are often referred to as “clamshell” containers or packages.
In one type of hinged tamper evident container the lid and base each have interlocking elements respectively located on or near the lid rim and base rim where the two rims meet when the container is sealed (i.e., at a non-hinged side or portion of the container). The interlocking element of the lid or base is conventionally located on a tab or flange extending from the rim of the lid or base. Either or both of the tabs are attached to their respective rims by a frangible section of plastic. When the lid and base are placed in initial sealing arrangement, the interlocking elements on or near the lid rim and base rim engage and lock together. In order to open the initially sealed container, the frangible section of one or both tabs must be ruptured so as to release the tab or tabs from the container. Because the interlocking sealing elements are located on the tabs, rupturing one or more tabs from the container disables the locking mechanism. The ruptured tab provides evidence of the container having been opened.
One shortcoming with the prior art food container described above is that the interlocked tabs can be cut from the container in clean fashion using scissors or another cutting implement so as to remove any indicia of the container having had a tamper evident mechanism.
In view of the issues presented by incorporating a tamper evident mechanism in the meeting rims of the hinged container, some manufacturers have incorporated tamper evident features as part of the structure that forms or includes the hinge. In these containers, the container is designed to require a severance near the hinge in order to unseal (initially open) the container. This construct make the hinge a single use hinge. These containers typically employ a square-shaped hinge arrangement (as seen from the side when the container is closed) in which the flange of the lid rim extends beyond the lid rim and then near-perpendicularly connects to a vertical segment that descends down from the lid flange. The vertical segment meets an extended portion of the base flange in similar near-perpendicular arrangement. The two flanges generally run parallel to each other and by their connection to the vertical segment form three sides of a square.
One example of a container with a square-shaped tamper evident hinge structure is shown in U.S. Pat. No. 7,073,680 (Boback, et al.). As can be seen in this patent, at the container's hinge area, the flange of the lid rim is vertically spaced above the flange of the base rim. A span of material (equal to the vertical spacing) adjoins to and descends from one end to the flange of the lid rim. The other end of the span of material adjoins to and ascends from the flange of the base rim. The span of material thus forms a strip of material connecting the lid rim flange and the base rim flange and operates to form hinge structure for the container. The lines of connection between the strip and the flanges are scored or include serial perforations such that the strip is a frangible section that can be torn away from the container after it is first sealed. With this type of tamper evident arrangement, one is left with a separate tear strip that must be disposed of and likely will not be recycled with the bulk of the container.
Another example of a clamshell container utilizing a square-shaped tamper evident hinge formation is shown in U.S. Published Patent Application No. 20120181280 (Barbier, et al). This reference discloses a hinge structure that is adapted to break by application of a squeeze force that causes the relative movement of two-adjacent sides (the top flange and the vertical span of material) that form the hinge arrangement.
Square-shaped hinge containers suffer from a variety of deficits. One is a tendency of the container not to remain fully open for purposes of filling the container. The memory of the square hinge mechanism is such that the lid tends to flop over and cover all or part of the base. Another deficit, at least as far as the Barbier container is concerned, is that the squeezing action required must move two adjacent, near perpendicular sides of the hinge structure and therefore the entire hinge structure must be effectively crushed in order to break the frangible line located at the bottom outside corner of the hinge structure. Thus, as is seen from the drawings in that published application, in order to rupture the frangible line, a squeezing force is applied to the entire box structure of the hinge area. This extended crushing motion may require the container to be stabilized with one's other hand in order to entirely rupture the frangible section. There is thus a need in the art for a re-closable plastic food container that is easy for end consumers to operate; combines reliable tamper evidence and defense against prying intrusion; and that uses a minimum of material to manufacture.